An antenna, as a component transmitting and receiving signals, is generally accommodated in a mobile phone and covered by a cover plate. However, with the popularity of the metallic appearance of the mobile phone, the radio frequency performance of the antenna may deteriorate due to a fully metalized cover plate of the mobile phone. Furthermore, an external antenna design in a metal cover plate can ingeniously enable a part of the metal cover plate to serve as an antenna which has a signal transmitting and receiving capability stronger than that accommodated in a mobile phone having a cover plate made from material other than metal, such that users can still access the internet or communicate normally even if signals are weak.
When an external antenna design is adopted, a slot should be defined in the cover plate, which is beneficial for the antenna. Radio Frequency requires that filler material in the slot be non-conductive so as to improve radiation performance of the antenna. In general, the slot is filled with plastic such as polyphenylene sulfite (PPS) or polybutylene terephthalate (PBT), while the other part of the cover plate is generally made of aluminum alloy and has an anodized appearance. However, the plastic in the slot has a color quite different from the anodized aluminum alloy, which seriously destroys unity of the cover plate. Therefore, the surfaces of the slot and the cover plate of the mobile phone still need to be improved.